For this reason, FDA guidelines call for a reduction in the irinotecan starting dose in patients with colorectal cancer with known UGT1A1 *28/*28 status27,28,30, and European Society for Medical Oncology guidelines recommend UGT1A1 genotyping in patients with metastatic colorectal cancer for whom an irinotecan dose >180 mg/m2 is planned and there is a suspicion of UGT1A1 deficiency, as reflected by low conjugated bilirubin31. This evidence concerns the gene UGT1A1 and colorectal cancer.